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ILEX Completes New Drug Application for Clofarabine; Filing Offers Hope to Children with Most Difficult-to-Treat Leukemias

SAN ANTONIO, March 31, 2004 -- ILEX(TM) Oncology, Inc. (Nasdaq:ILXO) announced today that it has submitted the final section of its New Drug Application (NDA) to the U.S. Food and Drug Administration (FDA) for clofarabine for the treatment of refractory or relapsed acute leukemia in children. In September 2003, clofarabine was granted fast-track status because of its potential to treat a serious, life-threatening condition and address an unmet medical need. ILEX submitted the first part of its "rolling" application to the FDA in October 2003 and has now delivered what the Company considers to be a completed NDA package to the FDA.

"This new drug application underscores the importance of developing new therapies for children with the most common forms of leukemia who have had no remaining treatment options," said ILEX CEO and President Jeff Buchalter. "Through the filing of clofarabine, ILEX is committed to providing new hope to treat these very sick children."

The filing was based on data from two pivotal acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) Phase II trials, which will be presented at the 40th American Society of Clinical Oncology annual meeting in June.

"In the clofarabine clinical trials, I have been able to offer hope to many children with very limited time left and no remaining therapeutic options," said lead clofarabine investigator Sima Jeha, MD, Director, Developmental Therapeutics, Division of Leukemia/Lymphoma, St. Jude Children's Research Hospital. "Pediatric patients and their families usually have to wait a long time before a novel treatment option is available to them and I'm encouraged to be part of an effort that has made children a priority in the oncology arena."

Clofarabine was previously granted orphan drug designation for the treatment of adult and pediatric ALL and AML by the FDA. In the U.S., orphan drug status guarantees seven years of market exclusivity for the orphan drug indication following the FDA's marketing approval.

In 2004, an estimated 3,200 new cases of pediatric leukemia will be diagnosed. Cure rates for pediatric leukemia have improved dramatically over the past several decades. However, children who do not respond to initial therapies have a very poor prognosis and long-term remissions are rare.

About Clofarabine
Clofarabine is a second generation of the drug class purine nucleoside analogs - or an improvement in the safety and efficacy of other drugs in this class - all inhibiting DNA production necessary for cancer cell growth. Bioenvision, Inc. (Amex: BIV) granted ILEX the right to develop clofarabine in the United States and Canada. Bioenvision is entitled to milestone payments tied to the development of the compound and is entitled to royalties on North American sales. As is its exclusive right, Bioenvision is developing clofarabine in the rest of the world. Bioenvision originally obtained clofarabine development and commercialization rights under patents held by Southern Research Institute.

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